Peduncles stipitate-glandular. Phyllaries stipitate-glandular, longer 14–17 mm. 2n = 54.

Flowering Jul–Sep. Disturbed sites, mostly wet, particularly in urban areas, roadside ditches, along streams; 0–1600. m; introduced; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask.; Alaska, Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Ky., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nev., N.H., N.J., N.Y., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Utah, Vt., Wash., Wis., Wyo.; Europe; widely introduced elsewhere.

Subspecies arvensis is considered a noxious weed in California, Idaho, Illinois, Iowa, Maryland, Minnesota, Nevada, North Dakota, South Dakota, and Wyoming.